The invention relates to an implant, in particular an intramedullary pin for treating a proximal fracture of the humerus, said pin having at least one distal and at least one proximal part, which are arranged so as to be displaceable axially in relation to one another to modify the length of the implant and which have guide surfaces cooperating with each other.
The fracture of the proximal portion of the humerus, i.e. the breaking of the head of the upper arm into two or more parts and/or of the adjoining upper arm shaft, is still a problem of fracture care which has not been finally solved in accident surgery. This is also shown by the plurality of different procedures, operative possibilities and implants which have been discussed and recommended for years in this context.
The shoulder is the most movable joint of the human body. In order to make this possible, the joint socket of the shoulder joint is scarcely developed. The guidance during movement and the stability are only achieved by the joint capsules, ligaments, musculature and tendons, which are attached directly to the upper arm head or in the immediate proximity.
In the case of a breakage of the upper arm head into two, but generally into several parts, typically the following situation occurs: The breakage zone between the upper arm head and upper arm shaft (subcapital fracture zone) is very unstable, the fragments are often displaced considerably. The parts of the upper arm head to which tendons are attached (tubercles), are not only dislocated by the trauma but also by the traction of the tendons. The piece bearing joint surfaces is tilted, owing to the lack of support. If the adjoining part of the upper arm shaft is also affected, a displacement of fragments can also take place here. In any case, however, a further increase to the instability occurs. In addition to this is the fact that the tuberculum majus, to which the essential tendons are attached for the movement of the upper arm, and which additionally offers an important support of the piece bearing the joint surface, almost always breaks up into several, partly very small pieces.
Furthermore, the fracture of the upper arm head is typically an injury which occurs primarily in older people. As a result of the poorer quality of the bone, implants often only find an insufficient hold here. A complete immobilization of the shoulder joint in a bandage is not possible, therefore after operative care, tractive, bending and shearing forces still also occur onto the subcapital fracture zone and on parts of the upper arm head or upper arm shaft.
In the weeks after the trauma, when the patient starts to move the arm again, a “collapsing” of the subcapital fracture zone always occurs. This is the prerequisite that the fracture is growing together. Only thereby are a rapid fracture healing and the avoidance of a pseudoarthrosis possible. Tractive forces of the tendons (rotator cuff) continue to act on parts of the upper arm head. If screws of implants do not find a good hold in the bone or if not all the pieces of bone are fixed by the implants in a stable manner with regard to movement, the danger exists that in the weeks after the operation, when musculature is used again, a secondary dislocation of fracture parts and/or osteosynthesis material occurs.
The osteosynthesis should be stable with regard to movement, in order to be able to begin the physical therapy as early as possible without the risk of secondary dislocation. In an older person namely a lengthy immobilization of the shoulder joint is connected with a shrinkage of the joint capsule and hence an often painful restriction to movement.
A removal of the implant should not be ordinarily necessary, because damage to the soft tissue can occur through a further operation. Furthermore, the rehabilitation is impaired in a negative manner by the necessary renewed postoperative protection.
The implants which are currently common, which are used for the care of these fractures, can be classified into two groups:
Semirigid implants, which primarily have the aim of fixing the subcapital fracture zone in the repositioned state, and which at the same time permit a collapsing of the fracture. The remaining fragments of the upper arm head are fixed here by screws. The advantages of this method lie in the good osseous healing of the subcapital fracture, because through the collapsing a certain compression occurs, which promotes the healing of the fracture. It is found to be disadvantageous that the screwed tubercles can still move easily in the first weeks. This is on the one hand because it is not possible to fix all the fragments by means of screws, and on the other hand because the screws find only a very little hold in the soft bone structure of the upper arm head and a screwing through of the opposite hard corticalis bearing the joint surface must be avoided, because the screw tips would then project into the joint. In the case of a dislocation of the tuberculum majus, however, the support of the part bearing the joint surface is also absent, whereby a tilting of the entire upper arm head is possible in the first days and weeks after the operation. Therefore, factures which are treated by these implants must often be fixed for a longer time by a bandage, which results in a restriction to the movement of the shoulder joint. Fractures which additionally also extend into the upper arm shaft can generally not be treated with these implants at all. Included among the semirigid implants are:
Spongiosa Screws, Drill Wires
The screws or drill wires can be positioned well in an ideal position, i.e. in a diverging position and at right angles onto the acting forces which are to be expected.
However, they often only find a poor hold in the bone spongiosa of the upper arm head. As a result of the poor anchoring possibilities, often a slipping of the fragments and of the screws or wires occurs upon movements in the shoulder joint. On the collapsing of the subcapital fracture, the implants can “slip back” in a lateral direction, whereby the fragment bearing joint surfaces can tilt again.
Drill Wires And Humerus Block
The block prevents the slipping back of the drill wires. On collapsing, the perforating of the drill wires through the joint surface into the joint can occur. This implant must always be removed after a few weeks in a second operation. The tubercles are provided with screws, for which the disadvantages described above apply.
Intramedullary Wires
Often, it is not possible to reposition the fracture or to fix the repositioned result. Here, also, the slipping of the wires can easily occur, either proximally through the joint surface or also in a distal direction. Here, also, the tubercles are provided with screws.
Helix Wire
The helix wire can compensate well for the collapsing of the subcapital fracture zone; perforation through the joint surface occurs very rarely. However, the same disadvantages apply as in the case of the intramedullary wires; with this implant, it is also not often possible to fix the rotation.
Rigid Implants
With these implants, generally a good reposition result can be achieved. The fixing of the tubercles is also generally possible to a better extent. On the one hand, because the fragments of the tuberculum majus are fixed through the surface of the plate, and on the other hand because the screws are not only fixed in the spongy bone, but also find a hold in the implant (plate, pin). However, these implants can not compensate for the movements occurring postoperatively. In the region of the subcapital fracture zone, a compression is not possible, therefore poor osseous healing and pseudoarthoses can occur here. If the arm is moved before the osseous healing, parts of the implants which are in fact fixed on the upper arm shaft can perforate through the joint surface on collapsing of the fracture or can cause the fracture pieces of the upper arm head to slip again.
Plate
The screws of the plate do in fact fine a good hold on the upper arm shaft, but little hold in the bone of the upper arm head. On postoperative moving, the dislocation or pulling out of these screws often occurs, whereby the reposition result is lost and the plate has to be removed again. Furthermore, through the areal compression of the plate onto the bone, the blood flow of the periosteum and hence the healing of the bone is disturbed.
Angle-stable Plate
The screws are fixed in the plate in an angle-stable manner and can not slip. However, they nevertheless do not find a good hold in the spongy bone. Especially the fragment of the upper arm head bearing joint surfaces can “detach” itself from the spongiosa screws of the plate and can tilt again. With a good osseointegration both into the upper arm head and also into the upper arm shaft, with a lack of subcapital healing a breakage of the plate can occur as a result of the movements in this zone. For the implantation of plates, a relatively large skin incision is necessary, with the disadvantages of soft tissue damage connected therewith.
Humerus Pin
As an intramedullary force carrier, the pin compensates well for all the forces which occur, and also a breakage of the pin never occurs. The surgical access is small, protects the soft tissues and the fracture zone is not additionally traumatized. However, the pin is fixed both in the upper arm head and also on the upper arm shaft and does not permit any collapsing in the subcapital fracture region. It can therefore happen that on collapsing of the subcapital fracture zone, the upper arm head or parts thereof are displaced over the pin in a caudal direction and therefore the pin or the locking screws project over the bone. If the screws can fix the upper arm head well, the pin prevents a sliding together of the subcapital fracture zone. Therefore, the compression of the fracture surfaces is absent and an absent fracture healing with persistent movement pain can occur.
Humerus Pin In Combination With Angle-Stable Plates (WO 2009/021624 A1)
The disadvantages of the intramedullary pin (risk of dislocation of the tuberculum minus, few screws for fixing the fragment bearing the joint surface) are minimized by the use of a small plate which fixes the tuberculum majus and is fixed on the pin by means of a rigid connection. The screws in the upper arm head are fixed in the plate in an angle-stable manner. The advantage is, without doubt, that the tuberculum majus is fixed in a distinctly better manner.
However, it remains as a disadvantage that, as in all the screws which are used, a holding of the screw thread in the opposite thin corticalis is only possible to a limited extent, so that a dislocation of the joint surface bearing fracture piece is still possible. As the plate is rigidly connected with the pin, on collapsing of the fracture in the subcapital zone, in the same way as with the humerus pin, a dislocation of the entire pin/plate construction can also occur in a cranial direction. By the relative higher placement of the plate, the “impingement syndrome” can occur here or, in the worse case, a perforation of the pin/plate construction through the upper arm head in a cranial direction.
At times, irrespective of the result of the operation, it can become necessary to subsequently replace an operated humerus head by a prosthesis. According to the prior art, to do this, an implant which may be present, which serves for the reposition and fixing of a humerus fracture, must be removed, which frequently proves to be difficult when the implant has grown securely into the bone. A corresponding operation entails an extensive impairment to the bone here and a considerable irritation to the soft tissue, so that the successful insertion of an implant is made difficult. It would therefore be desirable to be able to use a part of an inserted implant as a shaft for a prosthesis.